Tubular sensors for inline measurement of the properties of a fluid

ABSTRACT

An inline fluid properties measurement device that includes a tube defining an interior space that includes at least one non-cylindrical volume, and having a fluid entrance and exit, and capable of conducting fluid from the fluid entrance to the fluid exit, through the at least one non-cylindrical volume. An excitation and sensing transducer assembly is positioned to torsionally drive the tube and to sense torsional movement of the tube and a controller is programmed to drive the excitation and sensing transducer to drive the tube in torsion, thereby translating the fluid in the at least one non-cylindrical volume, and to sense torsional movement of the tube, thereby producing a sense signal. Finally, a signal analysis assembly responsive to the sense signal to form a measurement of at least one property of the fluid.

RELATED APPLICATIONS

This application is a continuation of application U.S. Ser. No.15/688,789, filed Aug. 28, 2017, which itself claims benefit ofprovisional application Ser. No. 62/379,953, filed on Aug. 26, 2016,which is incorporated by reference as if fully set forth herein.

BACKGROUND

Sensors for measuring the properties of a fluid in a manufacturingprocess are known. However, sensors that are placed in pipes carryingprocess fluids are particularly advantageous because they measure therelevant fluid properties—for example viscosity and density—at the pointof application, and so better represent these properties at the point ofapplication. Online measurements permit rapid adjustment of processparameters, enabling the operator to maintain process tolerances withminimal waste of material.

Among inline sensors, those that produce minimal obstruction to theflowing medium are particularly advantageous, from the standpoint ofcleanability, and reduced tendency to trap particulate components of thefluid medium that could cause a blockage and also influence theoperation of the sensor. Tubular sensors offer particular advantages inthis respect, since they can be placed in series with process piping,without the need of bypass lines or special measurement chambers thatintroduce unwanted obstructions into the process line.

Inline tubular sensors are well known, of which Coriolis mass flowmeters are perhaps the most widely employed. Coriolis meters usevibrating tubes to measure both mass flow and density. Of known Coriolismeters, a species thereof uses a straight tube vibrating transversely tomake the desired measurements. Of straight-tube Coriolis meters, thereare known methods for extracting information about the viscosity of theflowing medium, although this is generally considered a secondarymeasurement.

It is widely known that transverse vibrations in a straight tube aredifficult to isolate from the means used to mount the tube in itssupporting structure. Such supporting structures must be sufficientlyrigid and massive such that the vibrations of the tube are notinfluenced by forces incurred from installing the sensor in the processpipeline. In the case of viscosity measurement, where it is necessary tomeasure the mechanical damping of the tubular resonator, any loss ofenergy through the mounting structure has a negative impact on themeasurement of the viscosity of the fluid contained therein.

It is known that resonators vibrating torsionally are easier to decouplefrom their mounting structures because of the absence of the bendingforces exerted on such structures by transversely vibrating resonators.Tubular resonators for measuring fluid properties are disclosed in U.S.Pat. Nos. 4,920,787 and 6,112,581. U.S. Pat. No. 6,112,581, inparticular, uses a torsionally vibrating tube to measure viscosity, butis also vibrated transversely to measure density, which carries with itthe disadvantages described above of transversely vibrating resonators.

SUMMARY

The present invention consists of a method for measuring fluidproperties using a tubular resonator vibrating in torsion, whichmeasures density and viscosity of a fluid contained within it, whileproviding minimal obstruction to the flow of the fluid. Although themethod is described as measuring density and viscosity, it is alsocapable of measuring other fluid properties, such as flow rate,corrosion effects and tendency of the fluid to deposit materials onsolid structures with which they are in contact. The invention thereforehas additional applications in monitoring deposition of, for example,scale, hydrates, waxes, and asphaltenes in petroleum flow assuranceapplications. It is also applicable to measurement of corrosion inpipelines and other fluid conduits subject to corrosion by the mediathey conduct.

The present invention also encompasses a device to perform the method,the device also encompassing a number of species with related approachesto extending the measurement range and field of application of thedevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an isometric sectional view of a sensor, according to thepresent invention.

FIG. 1B is a sectional view of the resonator of FIG. 1, taken along line1B-1B of FIG. 1A, with a portion of the outer casing not shown.

FIG. 2A is an isometric sectional view of an alternative embodiment of aresonator, according to the present invention.

FIG. 2B is a sectional view of the resonator of FIG. 2A, taken alongline 2B-2B of FIG. 2A.

FIG. 3A is an isometric sectional view of another alternative embodimentof a resonator, according to the present invention.

FIG. 3B is a sectional view of the resonator of FIG. 3A, taken alongline 3B-3B of FIG. 3A.

FIG. 4 is an isometric sectional view of the resonator of FIG. 1A,showing further elements of a working resonator.

FIG. 5A is a sectional view of the excitation and sensing transducer ofFIG. 4, taken along line 5A-5A of FIG. 4, but with other elements of theresonator of FIG. 4 removed, for clarity of presentation.

FIG. 5B is a sectional view of the resonator of FIG. 4, taken along aview line horizontally orthogonal to line 5A-5A of FIG. 4.

FIG. 6 is a block diagram of an embodiment of a fluid sensor accordingto the present invention.

FIG. 7 is a graph showing resonance amplitude as a function offrequency, for both a high density and a low-density liquid with similarviscosities

FIG. 8 is a graph showing resonance amplitude as a function offrequency, for both a high viscosity and a low viscosity liquid withsimilar densities

FIG. 9 is a graph showing phase delay between a sinusoidal excitationand a resonant response, as a function of frequency, for both a highviscosity and a low viscosity liquid.

DETAILED DESCRIPTION

Definition: In the context of this application, a cylindrical volume isround in cross-section.

In broad overview, this application discloses several structures fortubular resonators that produce motion of the tube contentsperpendicular to the surface of the tube when the tube is driventorsionally, to permit separation of the effects of fluid density andviscosity. In this way, the advantages of a purely torsional resonatorcan be gained while simultaneously providing an inline sensor that issensitive to at least density and viscosity of the contained fluid.

Referring to FIGS. 1A and 1B, an Inline resonator 10 consists of atubular structure 12 mounted in a supporting casing 14 (a portion of theouter portion of casing 14 is not shown, in fact it goes all the wayaround), with the central section 16 of the tubular structure 12 beingflattened in such a manner as to provide a noncylindrical, generallyrectangular flow channel 16 with two arcuate sides (as shown in FIG. 1B.

Resonator 10 includes an excitation and sensing transducer assembly (seeFIG. 4) for both exciting and sensing torsional vibrations of thetubular structure around its central lengthwise axis. Types oftransducers include, but are not limited to, electromagnetic transducersand piezoelectric transducers and other combinations, for example anelectromagnetic excitation transducer with an optical pickup.

The resonant vibrations of the tubular torsionally resonant structure 12are modified by the fluid contained within it in two principal ways. Asthe tube vibrates torsionally, it shears the fluid in a thin boundarylayer close to the wall of the tube 12. The shear stresses produced bythis shearing motion are proportional to the viscosity of the fluid andtherefore extract energy from the vibrating tube at a rate dependent onthe fluid's viscosity.

Furthermore, because the cross-section of tube 12 is flattened,torsional motion about the lengthwise axis produces a motion of the wallperpendicular to its own interior surface, causing apparent additionalfluid mass to vibrate along with the tube 12, the additional fluid massbeing proportional to the fluid's density. The additional mass-loading,combined with the rotational inertia of the tube's vibrating section,decreases the torsional resonant frequency of the tubular resonator, inproportion to the density of the fluid.

In addition to providing means to shear and displace fluid within theresonant structure, resonator 10 includes inertial masses 18, typicallyin the form of disks, and mounting fixtures 20, also typically in theform of disks, affixed to the interior of casing 14 (FIG. 1), which actto vibrationally isolate the resonator 10 from its environment, therebyminimizing the effects of mounting forces on the resonant properties ofthe resonator 10. Inertial masses 18 are smaller in diameter than themounting fixtures 20 so as not to contact the casing 14. The inertialmasses 18 create well defined nodes on the flow tube 12, minimizing thetorsional displacement of the tube 12 on the section of the tube 12between the mounting fixtures 20 and the inertial masses 18, resultingin a decoupling of the torsional vibrations of the flow tube 12 fromsaid mounting fixtures 20.

Two further species of resonators meeting the criteria of both shearingand displacing fluid during torsional motion are disclosed asembodiments of this method. It should be understood that these aremerely exemplary of possible further embodiments.

Referring to FIGS. 2A and 2B, a second method utilizes a cylindricaltubular resonator 110, equipped with inertial masses 112 and mountingfixtures 114, and also provided with fins 116 attached to the innersurface of the tube 118 and projecting substantially radially inwardlytoward the rotational axis of the tube 118. The fins 116 impartperpendicular motion to the contents of tube 118 necessary to producemass loading by the fluid which modifies the resonant frequencyproportionally to the fluid density. FIG. 2A shows an embodiment withfour such fins 116, although it is understood that any radiallysymmetric arrangement would serve an identical function. FIG. 2B shows across section through the central part of the tube 118 showing thesubstantially radial disposition of the fins 116.

Radially symmetric fin patterns are used to avoid applying unbalancedtransverse forces on the contents of tube 118 that could excite unwantedtransverse vibrations. This precludes the use of a single radial fin116, although such radially asymmetric fin patterns could be used ifsuch modes were desired.

A third embodiment 210 of the resonator, also fitted with inertialmasses 212 and mounting fixtures 214, extends at least two of the radialvanes to create a longitudinal wall or partition 216 through at least aportion of the tube 218, as shown in FIGS. 3A and 3B. FIG. 3A shows alongitudinal section through a tube 218 with a single longitudinalpartition 216, while FIG. 3B shows a cross sectional view through thecenter of the longitudinally partitioned tube 210.

As shown in FIG. 4, the transducers consist of two magnet-coilassemblies 322 symmetrically disposed around the lengthwise planeparallel to the flattened tube surfaces 316, and corresponding permanentmagnets 324 fixed to surfaces 316. In one embodiment, a first one of thetransducers 322 may be used for excitation and a second one of thetransducers 322 may be used for sensing. In an alternative preferredembodiment, both transducers 322 may be used for both sensing andexcitation by alternately switching the coils between the excitation andthe sensing circuit (not shown), as disclosed in U.S. Pat. Nos.8,291,750 and 8,752,416. This is possible under the condition that theresonator 310 is always operated in such a manner that the vibrationinduced by the excitation persists long enough after cessation of theexcitation signal to permit evaluation of the persistent signal forestimation of the fluid properties of interest.

The transducer arrangement shown in FIG. 4 is one of many possibletransducer arrangements, but is shown here as being particularlysuitable for exciting and sensing torsional vibrations in theembodiments shown in this application. The operating principle isexplained with the help of FIG. 5A, in which the magnets 324 and coils326 are shown isolated from the resonator 310 and supporting structures,for clarity of presentation.

The two coils 326, disposed on either side of the lengthwise plane,carry currents I and I′ in opposite directions. The fields of the twomagnets 324 bonded to the flattened tube 316 surface are parallel to oneanother. The resultant Lorentz forces, F and F′, produce matchingtorsional forces on the tube, as shown in FIG. 5B, causing rotation.Conversely, a torsional motion of the flattened tube 316, moves magnets324, thereby inducing currents in the two coils 326 proportional to theangular velocity of the tube 316 about its longitudinal axis.

Referring, now, to FIG. 6, in a preferred embodiment, current from coils326 caused by movement of magnets 324 drives an analog-to-digitalconvertor circuit (A/D) 402, at the input of a signal processingassembly 400. The output of A/D 402 is fed into a memory 406, that is atthe input of a data processing assembly 405 and analyzed by a CPU 410that operates in accordance with a computer program stored in anon-transitory program memory 408. One output from the CPU 410 drives adigital-to-analog convertor circuit (D/A) 418 which drives drivingcircuitry 420, which amplifies the signal, and which drives coils 326.In an alternative embodiment, a first coil 326 drives the A/D convertor402 and a second coil 326 is driven by the D/A convertor 418 and in turndrives facing magnet 324. The CPU 410 could also be termed a controllerand is part of the signal processing assembly 400.

Referring to FIGS. 7, 8 and 9, the resonant properties of a resonatorthat interacts with a fluid such that it both shears and displaces thefluid are influenced by the resistance of the fluid to the shear anddisplacement. Fluid properties can be measured by varying the frequencyat which the resonator is excited by the transducer and measuring theeffect on phase delay and peak resonance. The frequency response of theresonator is influenced by mass loading in that its resonant frequencyis lowered as the mass loading by the fluid increases. The displacementof the resonant peak is therefore a measure for the density of thefluid, the resonant peak displacement being roughly linear with thedensity of the fluid. This is shown by the resonance diagrams in FIG. 7.

Increasing viscosity of the fluid lowers and broadens the resonant peak,the broadening and lowering being roughly proportional to the squareroot of the product of the fluid's viscosity and density. The broadeningand lowering of the peak are shown in FIG. 8.

Electronic means for measuring the damping and resonant frequency areknown. A method that is particularly suited to the measurement of theresonant properties is disclosed, for example, in U.S. Pat. No.8,291,750. In that method, a gated excitation signal excites theresonator at several phase values around its resonant frequency, and agated phase locked loop measures the frequencies at which the phasevalues occur. From the frequencies and the phase values, the resonantfrequency and width of the resonant peak may be calculated, from whichcalculated values a viscosity and a density may be derived.

The operation of this phase locked loop is shown in FIG. 9. The twolines at phases of 45° and 135° intersect the phase response curves atfrequencies F1 and F2 for the lower viscosity fluid, and at F1′ and F2′for the higher viscosity fluid. The phase locked loop alternately locksthe resonator to, for example, 45° and 135° and measures the resultingfrequency difference for the two-phase angles. The frequency differenceF2−F1 is smaller than the frequency difference F2′−F1′, beingapproximately proportional to the square root of the product of densityand viscosity of the fluid. Similarly, the value of the resonantfrequency, for which the phase angle is 90°, can be determined bysetting the phase locked loop to 90°, and measuring its resultantfrequency, the frequency being a measure for the density of the fluid.From these two measurements, F(90°) and F2−F1, both thedensity-viscosity product and the density may be calculated, from whichtwo quantities the dynamic viscosity can also be calculated.Furthermore, the density and dynamic viscosity may be used to calculatekinematic viscosity.

The invention claimed is:
 1. An inline fluid properties measurementdevice, comprising: (a) a tube, having an exterior surface that ismounted in and to a supportive casing, and defining an interior spacethat includes at least one non-circularly cylindrical volume, and havinga fluid entrance and exit that extends further than said casing, therebyproviding a free end for a pipe to be attached on either end to saidtube, so that all of the liquid flowing through said pipe flows throughsaid tube, and capable of conducting fluid from said fluid entrance tosaid fluid exit, through said at least one non-circularly cylindricalvolume; (b) an excitation and sensing transducer assembly positioned totorsionally drive said tube and to sense torsional movement of saidtube; (c) a controller programmed to drive said excitation and sensingtransducer to drive said tube in torsion, thereby translating said fluidin said at least one non-circularly cylindrical volume, and to sensetorsional movement of said tube, thereby producing a sense signal; (d) asignal analysis assembly responsive to said sense signal to form ameasurement of at least one property of said fluid; (e) whereby saidtube can be mounted in and form a part of a fluid pathway; and (f)wherein said excitation and sensing transducer includes an electromagnetassembly and an attached magnet assembly, attached directly to saidexterior surface of said tube and responsive to said electromagnetassembly to place a torquing force on said tube, and wherein saidelectromagnet assembly also senses movement of said attached magnetassembly, said electromagnetic assembly being longitudinally coincidentto said attached magnet assembly.
 2. The inline fluid propertiesmeasurement device of claim 1, wherein at least a portion of said tubeis non-circularly cylindrical, thereby defining a single non-circularlycylindrical interior volume.
 3. The inline fluid properties measurementdevice of claim 1, wherein said tube includes inwardly extending fins,thereby dividing said interior space into multiple non-circularlycylindrical volumes.
 4. The inline fluid properties measurement deviceof claim 1, wherein said tube includes at least one longitudinalpartition, thereby dividing said interior space into at least twoseparate non-circularly cylindrical volumes.
 5. The inline fluidproperties measurement device of claim 1, wherein said signal analysisassembly includes an analog to digital convertor and a data processingassembly.
 6. The inline fluid properties measurement device of claim 1,wherein said one property of said fluid is fluid density.
 7. The inlinefluid properties measurement device of claim 6, further measuringviscosity.
 8. The inline fluid properties measurement device of claim 1,further measuring a second fluid property.
 9. The inline fluidproperties measurement device of claim 1, wherein said electromagneticassembly includes a first electromagnet on a first side of said tube anda second electromagnet on a second side of said tube, opposed to saidfirst side of said tube, and wherein said attached magnet assemblyincludes a first magnet opposed to said first electromagnet and a secondmagnet opposed to said second electromagnet.
 10. The inline fluidproperties measurement device of claim 9, wherein said attached magnetsare permanent magnets.
 11. The inline fluid properties measurementdevice of claim 9, wherein said first electromagnet drives said firstattached magnet and said second electromagnet senses said secondattached magnet.
 12. The inline fluid properties measurement device ofclaim 9, wherein said first and second electromagnets simultaneouslydrive said permanent magnets, and repeatedly stop driving said permanentmagnets and sense movement of said permanent magnets, by producingcurrent in proportion to said movement.
 13. The inline fluid propertiesmeasurement device of claim 1, further including a pair of mountingfixtures, mounting said tube in said casing and a pair of inertialmasses, inward of said mounting fixtures, mounted to said tube and nottouching said casing.
 14. The inline fluid properties measurement deviceof claim 13, wherein said inertial masses and said mounting fixtures arein the form of disks.
 15. A method for measuring properties of a fluid,comprising: (a) providing an inline fluid properties measurement device,comprising: (i) a tube having an exterior surface that is mounted in andto a casing, and that defines an interior space that includes at leastone non-circularly cylindrical volume, and that has a fluid entrance andexit and is mounted into a fluid pathway, so that all of said fluidflowing through said fluid pathway flows through said tube; (ii) anexcitation and sensing transducer assembly positioned to torsionallydrive said tube and to sense torsional movement of said tube; (b)driving said excitation and sensing transducer assembly to drive saidtube in torsion, thereby translating and shearing said fluid in said atleast one non-circularly cylindrical volume and using said excitationand sensing transducer assembly to sense movement of said tube; (c)analyzing said sense signals to measure at least two fluid properties ofsaid fluid in said tube and; (d) wherein said excitation and sensingtransducer includes an electromagnet assembly and an attached magnetassembly, attached directly to said exterior of said tube and responsiveto said electromagnet assembly to apply a torquing force to said tube,and wherein said electromagnet assembly also senses movement of saidattached magnet assembly, said electromagnetic assembly beinglongitudinally coincident to said attached magnet assembly.
 16. Themethod of claim 15, wherein at least a portion of said tube isnon-circularly cylindrical, thereby defining a single non-circularlycylindrical interior volume.
 17. The method of claim 15, wherein saidtube includes inwardly extending fins, thereby dividing said interiorspace into multiple non-circularly cylindrical volumes.
 18. The methodof claim 15, wherein said tube includes at least one longitudinalpartition, thereby dividing said interior space into at least twoseparate non-circularly cylindrical volumes.
 19. The method of claim 15,wherein said two fluid properties are fluid density and viscosity. 20.The method of claim 15, wherein said electromagnet assembly includes afirst electromagnet on a first side of said tube and a secondelectromagnet on a second side of said tube, opposed to said first sideof said tube, and wherein said attached magnet assembly includes a firstmagnet opposed to said first electromagnet and a second magnet opposedto said second electromagnet.
 21. The method of claim 20, wherein saidattached magnets are permanent magnets.
 22. The method of claim 20,wherein said first electromagnet drives said first attached magnet andsaid second electromagnet senses said second attached magnet.
 23. Themethod of claim 20, wherein said first and second electromagnetssimultaneously drive said permanent magnets, and repeatedly stop drivingsaid permanent magnets and sense movement of said permanent magnets, byproducing current in proportion to said movement.
 24. The method ofclaim 15, wherein said tube is attached inside said casing by a pair offixtures at opposed ends and further wherein a pair of inertial massesare attached about said tube, inward of said fixtures, to help isolatetube vibrations.
 25. The method of claim 24, wherein said inertialmasses are in the form of disks.